Protesters opposing Egyptian President Mohammed Morsi, one wears a Guy Fawkes mask, chant slogans during a demonstration that started in front of el-Nour mosque, background, in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president staged rival rallies in the nation's capital Tuesday, four days ahead a nationwide referendum on a contentious draft constitution.(AP Photo/Nasser Nasser)

Egyptian Army tanks, left, deploy outside the presidential palace as Egyptian protesters gather during a demonstration against President Mohammed Morsi in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president staged rival rallies in the nation's capital Tuesday, four days ahead a nationwide referendum on a contentious draft constitution. (AP Photo/Hassan Ammar)

A Supporter of the Muslim Brotherhood and Egyptian President Mohammed Morsi chants slogans during a demonstration, in Cairo, Egypt, Tuesday, Dec. 11, 2012. Islamists led by Morsi's Muslim Brotherhood group have called a demonstration to back the president's decision to hold a referendum on the new constitution on December 15. Opposition groups have rejected the constitution as undemocratic and want the vote canceled. The woman's badge reads in Arabic " the Quran is our constitution."(AP Photo/Hassan Ammar)

Photo: Hassan Ammar, Associated Press

A Supporter of the Muslim Brotherhood and Egyptian President...

A Supporter of the Muslim Brotherhood and Egyptian President... Photo-3879744.53773 - SFGate

Supporters of Egyptian President Mohammed Morsi, from Al Azhar schools chant slogans during a demonstration in Cairo, Egypt, Tuesday, Dec. 11, 2012. Islamists led by Morsi's Muslim Brotherhood group have called a demonstration to back the president's decision to hold a referendum on the new constitution on December 15. Opposition groups have rejected the constitution as undemocratic and want the vote canceled. Arabic on the paper reads, "yes to the constitution." (AP Photo/Hassan Ammar)

Egyptian army soldiers stand guard during a demonstration in front of the presidential palace in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president were flocking to key locations in the nation's capital ahead of rival mass rallies Tuesday, four days before a nationwide referendum on a contentious draft constitution. (AP Photo/Petr David Josek)

Photo: Petr David Josek, Associated Press

Egyptian army soldiers stand guard during a demonstration in front...

Egyptian army soldiers stand guard during a demonstration in front... Photo-3879743.53773 - SFGate

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Protesters chant and dance in front of the presidential palace as one protester holds a flare during a demonstration in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president staged rival rallies in the nation's capital Tuesday, four days ahead a nationwide referendum on a contentious draft constitution. (AP Photo/Petr David Josek)

Egyptian riot police guard in front of the presidential palace in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president were flocking to key locations in the nation's capital ahead of rival mass rallies Tuesday, four days before a nationwide referendum on a contentious draft constitution. (AP Photo/Petr David Josek)

Protesters opposing Egyptian president Mohammed Morsi, one wearing a Guy Fawkes mask, chant slogans and carry a national flag with Arabic that reads "January 25," during a demonstration in front of el-Nour mosque, background, in Cairo, Egypt, Tuesday, Dec. 11, 2012. Thousands of opponents and supporters of Egypt's Islamist president staged rival rallies in the nation's capital Tuesday, four days ahead a nationwide referendum on a contentious draft constitution.(AP Photo/Nasser Nasser)

Protesters opposing Egyptian president Mohammed Morsi fly national flags and chant slogans during a demonstration in front of the presidential palace in Cairo, Egypt, Tuesday, Dec. 11, 2012. Islamists led by Morsi's Muslim Brotherhood group have called a demonstration to back the president's decision to hold a referendum on the new constitution on December 15. Opposition groups have rejected the constitution as undemocratic and want the vote canceled. Arabic on the posters reads, "yes to Islamic law." (AP Photo/Nasser Nasser)

Egyptian opposition supporters shout slogans during a march heading to the Presidential Palace in Cairo to protest against the upcoming referendum on the new draft constitution on December 11, 2012. Protesters gathered in Cairo for rival rallies over a deeply disputed constitutional referendum proposed by Egypt's Islamist president, Mohamed Morsi, raising fears of street clashes. TOPSHOTS/AFP PHOTO/GIANLUIGI GUERCIAGIANLUIGI GUERCIA/AFP/Getty Images

Photo: Gianluigi Guercia, AFP/Getty Images

Egyptian opposition supporters shout slogans during a march heading...